Photon Propagation Research Articles

Propagation of photoluminescence photons in fluorescent optical fibers

Propagation of photoluminescence photons in fluorescent optical fibers

Non‐destructive analysis of concentration profiles in turbid media using micro‐spatially offset Raman spectroscopy: A physical model

AbstractWe introduce an analytical physical description of micro‐spatially offset Raman spectroscopy (micro‐SORS) experiments in turbid samples with a special emphasis on its use for studying the penetration depth of chemical species (agents) into a matrix. Such samples exhibit varying concentration gradients with depth and reflect typical situations encountered in Cultural Heritage framework. The experiments aim at yielding the variations (trends) of the Raman intensity ratio of the agent and matrix marker bands, , with increasing micro‐SORS defocusing distance . The physical model shows that can be expressed as a function of the concentration profiles of the analytes. The analysis makes use of Monte Carlo simulation results of the propagation of photons in turbid media. Despite the introduced approximations, the obtained formulas provide an insightful tool that allows justifying the observed trends and facilitates the interpretation of micro‐SORS data and systematic comparison among different samples. Basic comparison with previously published experimental micro‐SORS data indicates good consistency. The obtained relationships could also be useful for a semi‐quantitative estimate of concentration profiles in unknown samples.

Quantifying tissue optical properties of human heads in vivo using continuous-wave near-infrared spectroscopy and subject-specific three-dimensional Monte Carlo models.

.Significance: Quantifying subject-specific optical properties (OPs) including absorption and transport scattering coefficients of tissues in the human head could improve the modeling of photon propagation for the analysis of functional near-infrared spectroscopy (fNIRS) data and dosage quantification in therapeutic applications. Current methods employ diffuse approximation, which excludes a low-scattering cerebrospinal fluid compartment and causes errors.Aim: This work aims to quantify OPs of the scalp, skull, and gray matter in vivo based on accurate Monte Carlo (MC) modeling.Approach: Iterative curve fitting was applied to quantify tissue OPs from multidistance continuous-wave NIR reflectance spectra. An artificial neural network (ANN) was trained using MC-simulated reflectance values based on subject-specific voxel-based tissue models to replace MC simulations as the forward model in curve fitting. To efficiently generate sufficient data for training the ANN, the efficiency of MC simulations was greatly improved by white MC simulations, increasing the detectors’ acceptance angle, and building a lookup table for interpolation.Results: The trained ANN was six orders of magnitude faster than the original MC simulations. OPs of the three tissue compartments were quantified from NIR reflectance spectra measured at the forehead of five healthy subjects and their uncertainties were estimated.Conclusions: This work demonstrated an MC-based iterative curve fitting method to quantify subject-specific tissue OPs in-vivo, with all OPs except for scattering coefficients of scalp within the ranges reported in the literature, which could aid the modeling of photon propagation in human heads.

Simulation of Radiative Transfer Within X-ray Microcalorimeter Absorbers

We present Monte Carlo simulations of radiative transfer within the absorbers of X-ray microcalorimeters, utilizing a numerical model for the photon propagation and photon absorption process within the absorber structure. In our model, we include effects of Compton scattering off bound electrons and fluorescence. Scattered or fluorescence photons as well as Auger and photoelectrons escaping the absorber can result in partial energy depositions. By implementing a simplified description of the physical processes compared to existing comprehensive particle transport software frameworks, our model aims to provide representative results at a small computational effort. This approach makes it possible to use our model for quick assessments, parametric studies, and application in other Monte Carlo-based instrument simulators like SIXTE, a software package for X-ray astronomical instrumentation. To study the impact of the energy loss effects on the spectral response of a microcalorimeter, we apply our model to the sensors of the cryogenic X-ray spectrometer X-IFU onboard the future Athena X-ray observatory.

Теоретическое исследование влияния рассеивающей среды, состоящей из атомов калия, на время затухания люминесцентного сигнала с использованием метода Монте-Карло

The study solves the problem of the luminescent photons propagation in a resonantly absorbing medium consisting of atoms of the studied substance and a buffer inert gas. The Monte Carlo method was used in numerical experiments carried out to simulate real processes that occur in a chamber designed to determine the lifetime of an individual atom in an excited state by the method of measuring the luminescence intensity decay time. Findings of the research show that when luminescent photons are repeatedly scattered (scattering means the process of absorption and re-emission of a photon by an atom) in a medium, the luminescence decay time noticeably increases, reaching a value greater than the average lifetime of an individual atom in an excited state. The reflection of photons from the walls that make up the chamber can lead to errors in measuring the lifetime. The process of luminescence decay is studied theoretically for various detunings of the laser frequency from the resonant transition frequency. A three-level model of the atom and a model of complete frequency redistribution were applied. The study describes an algorithm based on the Monte Carlo method, which is used to model the three-level population kinetics, laser radiation transfer, radiation trapping, and frequency redistribution

Nonreciprocal Single-Photon Band Structure.

We study a single-photon band structure in a one-dimensional coupled-resonator optical waveguide that chirally couples to an array of two-level quantum emitters (QEs). The chiral interaction between the resonator mode and the QE can break the time-reversal symmetry without the magneto-optical effect and an external or synthetic magnetic field. As a result, nonreciprocal single-photon edge states, band gaps, and flat bands appear. By using such a chiral QE coupled-resonator optical waveguide system, including a finite number of unit cells and working in the nonreciprocal band gap, we achieve frequency-multiplexed single-photon circulators with high fidelity and low insertion loss. The chiral QE-light interaction can also protect one-way propagation of single photons against backscattering. Our work opens a new door for studying unconventional photonic band structures without electronic counterparts in condensed matter and exploring its applications in the quantum regime.

Photon Characteristics and Behavior under Refractive Index

The effective mass, energy and momentum of photon in medium is described. The photon has both kinetic and potential energy and displays an effective mass when travelling through a medium. The photon is a type of elementary particle that serves as the quantum of the electromagnetic field and is explained through equations to have an elastic constant, volume, momentum, force, power and zero rest mass. The theory that photons a massless only applies to rest mass. A photon undergoes different dynamics such as strain and changes in effective mass under the influence of the refractive index that gives rise to a refractive force. This study synthesizes some properties of energy such as elastic constant, weight, and volume in order to explain the nature of photons and photon dynamics under refractive index. In this study, a helical spring model has been used to describe the behavior of a photon in the medium. The model connects together the exhibited properties such as energy, effective mass, spin, elastic constant and volume. Further explanation is given to the effect of gravitational force on wavelength and refractive index of air, and how gravitational force causes red and blue shifts in photon propagation. The quantization of energy has been extended to the quantization of space, time and matter. This study is consistent and consolidates the existing classical and quantum theories. There are further potential applications in optical communication, quantum cryptography, quantum optics, and medicine, especially in the use of two-photon excitation microscopy and photodynamic therapy.

Spontaneous parametric down-conversion: Revisiting the parameters of transverse entanglement outside the near zone

The reduced density matrix ${\ensuremath{\rho}}_{r}(x,{x}^{\ensuremath{'}})$ of the transverse biphoton state beyond the near zone is found to be real on and only on diagonals in the plane of the photon's transverse coordinates $(x,{x}^{\ensuremath{'}})$. This remarkable feature is found to occur at any distances of photon propagation with diffraction spreading completely taken into account. The functions of the reduced density matrix at two orthogonal diagonals, ${\ensuremath{\rho}}_{r}(x,x)$ and ${\ensuremath{\rho}}_{r}(x,\ensuremath{-}x)$, are considered as the only two complementary single-particle distributions generated by the reduced density matrix. The ratio of widths of these two distributions is interpreted as the new entanglement parameter ${R}_{\mathrm{diag}}$ which is found to be very close to and completely compatible with the Schmidt entanglement parameter $K$.

Graphics-processing-unit-accelerated Monte Carlo simulation of polarized light in complex three-dimensional media.

.SignificanceMonte Carlo (MC) methods have been applied for studying interactions between polarized light and biological tissues, but most existing MC codes supporting polarization modeling can only simulate homogeneous or multi-layered domains, resulting in approximations when handling realistic tissue structures.AimOver the past decade, the speed of MC simulations has seen dramatic improvement with massively parallel computing techniques. Developing hardware-accelerated MC simulation algorithms that can accurately model polarized light inside three-dimensional (3D) heterogeneous tissues can greatly expand the utility of polarization in biophotonics applications.ApproachHere, we report a highly efficient polarized MC algorithm capable of modeling arbitrarily complex media defined over a voxelated domain. Each voxel of the domain can be associated with spherical scatters of various radii and densities. The Stokes vector of each simulated photon packet is updated through photon propagation, creating spatially resolved polarization measurements over the detectors or domain surface.ResultsWe have implemented this algorithm in our widely disseminated MC simulator, Monte Carlo eXtreme (MCX). It is validated by comparing with a reference central-processing-unit-based simulator in both homogeneous and layered domains, showing excellent agreement and a 931-fold speedup.ConclusionThe polarization-enabled MCX offers biophotonics community an efficient tool to explore polarized light in bio-tissues, and is freely available at http://mcx.space/.

Combined Coulombic and magnetic contributions to dispersion in e + C12 collisions

Dispersion corrections to elastic electron scattering from a $^{12}\mathrm{C}$ nucleus are calculated within the second-order Born approximation. Three strong transient nuclear excitations are considered, at 4.439 MeV $({2}^{+})$, 17.7 MeV $({1}^{\ensuremath{-}}),$ and 23.5 MeV $({1}^{\ensuremath{-}})$. The Friar-Rosen-type Coulomb term is supplemented with the transverse part of the photon propagator. It is found that the dispersive cross-section changes in the first diffraction minimum reach nearly 10%, rising more slowly with collision energy beyond 400 MeV. Magnetic scattering can be strong for the individual excited states and lowers the dispersion effect considerably at energies below 400 MeV. However, it contributes at most 10% at the higher energies investigated.

Nondipole Time Delay and Double-Slit Interference in Tunneling Ionization.

Recently two-center interference in single-photon molecular ionization was employed to observe a zeptosecond time delay due to the photon propagation of the internuclear distance in a molecule [Grundmann etal., Science 370, 339 (2020)SCIEAS0036-807510.1126/science.abb9318]. We investigate the possibility of a comparable nondipole time delay in tunneling ionization and decode the emerged time delay signal. With the here newly developed Coulomb-corrected nondipole molecular strong-field approximation, we derive and analyze the photoelectron momentum distribution, the signature of nondipole effects, and the role of the degeneracy of the molecular orbitals. We show that the ejected electron momentum shifts and interference fringes efficiently imprint both the molecule structure and laser parameters. The corresponding nondipole time delay value significantly deviates from that in single-photon ionization. In particular, when the two-center interference in the molecule is destructive, the time delay is independent of the bond length. We also identify the double-slit interference in tunneling ionization of atoms with nonzero angular momentum via a nondipole momentum shift.

Hyperspectral image feature region of solution composition analysis method based on multidimensional spectra

Redundant information is inevitable when acquisition of high-dimension spectra, which contribute to the overfitting.In order to effectively reduce the dimensions of multi-dimensional spectral data and improve the accuracy of spectral detection of complex solution components, a method based on the gradient distribution of the multi-dimensional spectral image is proposed in this paper, aiming to extract the feature region, which is highly correlated with the solution concentration. In this research, firstly, photon propagation simulations in the wedge sample were performed using Monte Carlo, and the image of multi-dimensional spectra under different optical parameters was obtained. Furthermore, a method of extracting the position of the feature region based on the gradient distribution is proposed, according to the distribution characteristics of the image. Subsequently, a series of experiments were carried out of the visible-near-infrared spectra of 39 groups of mixed solutions, which composed of India Ink and Intralipid of sequential changed concentrations, to reveal the effectiveness of the feature region. The regression models for prediction of Intralipid concentration were developed by partial least square regression (PLSR). In contrast to the traditional spectral analysis method, the dimensionality of data was reduced to 1/9, by extracting the feature region of the multi-dimensional spectral data, while the average correlation coefficient (Rp) of prediction set reached 98.87%, and the average mean square error (RMSEP) of prediction set was 0.1502, showing an increase of 0.12% in Rp and a decrease of 6.12% in RMSEP, respectively. The results showed that models incorporating the feature region, improved the accuracy of component analysis of complex solutions with high-concentration and also the analysis speed and robustness of the model. A rapid, non-invasive, low-cost method is proposed in this paper, using visible-near-infrared spectroscopy with the wedge sample to analyze the components of complex solutions.

Reabsorption-free luminescent solar concentrator based on environmentally friendly cesium copper halide nanocrystals

Luminescent solar concentrator (LSC) based on colloidal nanocrystals (NCs) is the key component of building integrated photovoltaics (BIPVs). But strong reabsorption effect, or expensive/toxic components (e.g., In, Cd, or Pb) included in NCs hinder their applications. In this study, we fabricated low-cost, non-toxic LSCs based on cesium copper halide (Cs3Cu2X5, X = I or Cl) NCs. These materials possessed highly efficient self-trapped exciton emission with a large Stokes shift, with the consequent LSCs exhibiting clear reabsorption-free features with edge efficiencies close to the theoretical limits (∼70%) with varying device sizes. Furthermore, waveguiding PV devices consisting of above LSCs (8 × 8 × 0.5 cm3) and commercial polysilicon PV cells exhibit power conversion efficiencies (PCEs) of up to 1.8%. In addition to the waveguiding effect on luminescent photons, these excellent PCEs were confirmed induced by the scattering of visible solar photons. These results clearly illustrated the photon propagation mechanism in LSCs based on Cs3Cu2X5 NCs or similar colloidal NCs. The obtained PCEs in the range 0.8%–2.0% imply considerable potential for fabricating practical PV products with high output per Si PV unit area and low cost.

Enhance the delivery of light energy ultra-deep into turbid medium by controlling multiple scattering photons to travel in open channels

Multiple light scattering is considered as the major limitation for deep imaging and focusing in turbid media. In this paper, we present an innovative method to overcome this limitation and enhance the delivery of light energy ultra-deep into turbid media with significant improvement in focusing. Our method is based on a wide-field reflection matrix optical coherence tomography (RM-OCT). The time-reversal decomposition of the RM is calibrated with the Tikhonov regularization parameter in order to get more accurate reversal results deep inside the scattering sample. We propose a concept named model energy matrix, which provides a direct mapping of light energy distribution inside the scattering sample. To the best of our knowledge, it is the first time that a method to measure and quantify the distribution of beam intensity inside a scattering sample is demonstrated. By employing the inversion of RM to find the matched wavefront and shaping with a phase-only spatial light modulator, we succeeded in both focusing a beam deep (~9.6 times of scattering mean free path, SMFP) inside the sample and increasing the delivery of light energy by an order of magnitude at an ultra-deep (~14.4 SMFP) position. This technique provides a powerful tool to understand the propagation of photon in a scattering medium and opens a new way to focus light inside biological tissues.

Enhanced TEMPO Algorithm for Quantum Path Integrals with Off-Diagonal System-Bath Coupling: Applications to Photonic Quantum Networks

Multitime system correlation functions are relevant in various areas of physics and science, dealing with system-bath interaction including spectroscopy and quantum optics, where many of these schemes include an off-diagonal system bath interaction. Here we extend the enhanced time-evolving matrix product operator (eTEMPO) algorithm for quantum path integrals using tensor networks [Phys. Rev. Lett. 123, 240602 (2019)PRLTAO0031-900710.1103/PhysRevLett.123.240602 to open quantum systems with off-diagonal coupling beyond a single two level system. We exemplify the approach on a coupled cavity waveguide system with spatially separated quantum two-state emitters, though many other applications in material science are possible, including entangled photon propagation, photosynthesis spectroscopy, and on-chip quantum optics with realistic dissipation.

On-shell electric-magnetic duality and the dual graviton

Using on-shell amplitude methods, we explore four-dimensional electric-magnetic duality and its double copy. We show explicitly that the on-shell scattering amplitudes know about ``dual'' photons (and dual gravitons), that the off-shell photon propagator double-copies to the graviton propagator, and that the magnetic part of the propagator is essential for the double copy to hold. We also show that there is an equivalent gravitomagnetic part of the graviton propagator, which is essential in giving rise to solutions with either angular momentum or NUT charge. Furthermore, we comment on the so-called Weinberg paradox, which states that scattering amplitudes involving the mixing of electric and magnetic monopoles cannot be Lorentz invariant, and would seem to preclude the existence of the 't Hooft--Polyakov (topological) monopole. We trace this paradox to the magnetic part of the propagator, showing that it can be eliminated if one restricts the scenario to proper orthochronous Lorentz transformations. Finally, we compute the fully relativistic cross section for arbitrary spin dyons using the recently formulated on-shell duality transformation, and we show that this is always fully Lorentz invariant.

Organic Branched Heterostructures with Optical Interconnects for Photonic Barcodes

AbstractOptical interconnects exhibit superior potential in the precise regulation of photon transmission for organic photonic circuits. However, the rational design of well‐defined organic heterostructures toward active optoelectronics remains challenging. Herein, we designed organic branched heterostructures (OBHs) with accurate spatial organization for optical interconnection. Notably, the precise regulation of OBHs has been controllably achieved including the trunk morphologies and the branched microwire number. Significantly, these as‐prepared OBHs inherently exhibit the multichannel coupling outputs and the excitation position‐dependent waveguide characteristics, leading to various outcoupling signals with tunable intensity and emission colors. The optical interconnects are realized due to the occurrence of exciton conversion and photon propagation between branch and trunk at the heterojunction, benefiting the application possibilities of two‐dimensional (2D) optical barcodes.

Organic Branched Heterostructures with Optical Interconnects for Photonic Barcodes.

Optical interconnects exhibit superior potential in the precise regulation of photon transmission for organic photonic circuits. However, the rational design of well-defined organic heterostructures toward active optoelectronics remains challenging. Herein, we designed organic branched heterostructures (OBHs) with accurate spatial organization for optical interconnection. Notably, the precise regulation of OBHs has been controllably achieved including the trunk morphologies and the branched microwire number. Significantly, these as-prepared OBHs inherently exhibit the multichannel coupling outputs and the excitation position-dependent waveguide characteristics, leading to various outcoupling signals with tunable intensity and emission colors. The optical interconnects are realized due to the occurrence of exciton conversion and photon propagation between branch and trunk at the heterojunction, benefiting the application possibilities of two-dimensional (2D) optical barcodes.

VoxDMRN: a voxelwise deep max-pooling residual network for bioluminescence tomography reconstruction.

Bioluminescence tomography (BLT) has extensive applications in preclinical studies for cancer research and drug development. However, the spatial resolution of BLT is inadequate because the numerical methods are limited for solving the physical models of photon propagation and the restriction of using tetrahedral meshes for reconstruction. We conducted a series of theoretical derivations and divided the BLT reconstruction process into two steps: feature extraction and nonlinear mapping. Inspired by deep learning, a voxelwise deep max-pooling residual network (VoxDMRN) is proposed to establish the nonlinear relationship between the internal bioluminescent source and surface boundary density to improve the spatial resolution in BLT reconstruction. The numerical simulation and in vivo experiments both demonstrated that VoxDMRN greatly improves the reconstruction performance regarding location accuracy, shape recovery capability, dual-source resolution, robustness, and in vivo practicability.

Simulated assessment of light transport through ischaemic skin flaps

Currently, free flaps and pedicled flaps are assessed for reperfusion in postoperative care using colour, capillary refill, temperature, texture, and Doppler signal (if available). While these techniques are effective, they are prone to error due to their qualitative nature. In this research, different wavelengths of light were used to quantify the response of ischaemic tissue. The assessment provides indicators that are key to developing a point-of-care diagnostic device that is capable of observing reduced perfusion quantitatively. Detailed optical models of the layers of the skin were set up and appropriate optical properties assigned, with due consideration of melanin and haemoglobin concentration. A total of 24 models of healthy, perfused and perfusion-deprived tissue were used to assess the responses when illuminated with visible and near-infrared wavelengths of light. In addition to detailed fluence maps of photon propagation, a simple mathematical model is proposed to assess the differential propagation of photons in tissue; the optical reperfusion factor (ORF). The results show clear advantages of using light at longer wavelengths (red, near-infrared) and the inferences drawn from the simulations hold significant clinical relevance. The simulated scenarios and results consolidate the belief in a multi-wavelength, point-of-care diagnostic device, and inform its design to quantify blood flow in transplanted tissue. The modelling approach is applicable beyond the current research and can be used to investigate other medical conditions in the skin that can be mathematically represented. Through these, additional inferences and approaches to other point-of-care devices can be realised.